The present invention relates to an accessory device connectable to a specimen-carrier table of the non-eucentric type for the acquisition, by means of a scanning electron microscope, of images taken in an angularly offset manner for stereoscopic examination of a specimen.
Stereoscopic analysis by scanning electron microscope makes it possible to effect measurement in three dimensions and to detect, for example, the roughness parameters of irregular surfaces with very high magnification.
Stereoscopic analysis permits observation of a specimen with a perspective view, and in anaglyph (with three-dimensional vision by means of the use of suitable glasses). This latter possibility allows an immediate xe2x80x9creadingxe2x80x9d of the surface morphology of the specimen, making it possible to overcome the difficulties which often arise in the distinction between ridges and valleys of the surface of specimens under analysis.
In general, as is known, the process of stereoscopic analysis involves the acquisition of two images of the specimen, obtained by turning the specimen about a horizontal axis essentially orthogonal to the interocular line of the observer. These images are then superimposed. By means of a processor for the treatment and presentation of images, provided with suitable software, the anaglyph is presented on a display. The processor further allows a calculation of the microroughness parameters.
For stereoscopic analysis with scanning electron microscope a specimen-carrier table of eucentric type is sometimes utilised, which allows six degrees of freedom in the movement and which is formed in such a way as to maintain the position of the point of impact between the electron beam and the specimen essentially unaltered, even upon variation of the spatial co-ordinates of this latter. This property, and the possibility of turning the specimen, by rotation about the Y axis, of obtaining three dimensional stereoscopic analysis is particularly easy and rapid in that the two images detected with different angles of inclination of the electron beam do not require any movements along the X, Y and Z axes for their superimposition.
Specimen-carrier tables of eucentric type are however extremely expensive. For this reason scanning electron microscopes are very often provided with a non-eucentric table, which is rather more economical.
Specimen-carrier tables of non-eucentric type do not allow turning of the specimen about the Y axis, which operation is necessary for taking stereoscopic images. Nor is it possible to maintain unaltered the position of the point of incidence of the electron beam on the specimen upon variation of the spatial co-ordinates of this latter.
In view of the above, stereocscopic analysis with a specimen-carrier table of non-eucentric type is extremely laborious. It requires electronic rotation of the image through 90xc2x0, which then makes it possible to rotate the specimen in a virtual manner about the Y axis by acting on the rotation command about the X axis. The exchange of movements about the X and Y axes renders this manoeuvre unnatural and therefore difficult, in particular when working at very high magnifications.
The object of the present invention is to provide a device which allows stereoscopic images to be taken in an easy manner using a non-eucentric specimen-carrier table.
This object is achieved according to the invention with an accessory device comprising a support structure distinct and separate with respect to said specimen-carrier table, said support structure being comprised of metal material having a connection portion for detachably connecting the support structure to the movable member of the specimen-carrier table, and a support portion having a support surface which, when the structure is coupled to the movable member of the table, extends in a plane parallel to the axis of rotation in such a way that, after rotation of the movable member of the table through 90xc2x0 about the second axis, a subsequent rotation of the movable member about its own axis is able to cause the surface to turn about the third axis.